In recent years, portable computing devices including smartphones, tablets and notebooks have increased their computing power, screen resolution and display frame rate. These advancements have been enabled by sub-micron range silicon technology approaching 10 nm and below and allowing the formation of ultra-narrow gate structures. Ultra-narrow gate structures exhibit increased leakage current for each transistor.
In view of the fact that central processing units (CPUs) and graphical processing units (GPUs) are composed from multiple hundred million transistors, the leakage current of a modern microprocessor is significant. To reduce battery consumption, the embedded computing cores are typically disconnected from the power supply as often as possible. As a result, the required computing power is provided within short bursts of operation. Hence, the power profile of a modern mobile computing device is dominated by relatively long periods of standby currents in the mA range, interrupted by pulses of high peak currents (in the 20 A and higher range).
Smartphones and tablet computers are typically powered with a Li-Ion battery pack having a nominal output voltage of 3.6V. The CPU and GPUs produced from silicon technology with gate lengths of 10 nm and below requires a supply voltage of about 0.9V. The corresponding voltage step-down converter needs to optimize its efficiency around a typical Vout/Vin conversion ratio of 0.9V/3.6V=0.25. For such a conversion ratio traditional 2-levels and 3 levels buck converters exhibit significant conversion losses. The Dual-Stage 3-level capacitive divider as described in the publication titled “Zero Inductor Voltage Multilevel Bus Converter” IEEE 2018 by Samuel Webb, is unregulated and provides a conversion ratio of 0.25 only. However, a modified control system can be designed to regulate the output voltage with a conversion ratio above and below 0.25. Such a system however would still be limited by significant losses above and below 0.25. Therefore, there is a need for a power converter with reduced losses when operating with high conversion ratios.